A wildlife charity has renewed calls for oil additive PIB to be reclassified by the International Maritime Organisation to prohibit discharges at sea after “a whole generation of seabirds” died.
Hundreds of dead and distressed birds have been found washed up along the south west of England's coastline during the last week, two months after a similar spill caused widespread destruction to marine life.
Animal charities said the birds - mostly guillemots but also a smaller number of razorbills and puffins - have been found covered in a sticky, oily substance on beaches across Cornwall, Devon and Dorset.
The Devon Wildlife Trust said that the proportion of dead birds among those washed up has increased, with hundreds of stricken seabirds found on beaches around the West Country over the weekend.
Abby Crosby, marine conservation officer for Cornwall Wildlife Trust, said: "It has been a terribly sad time for everyone seeing these beautiful birds washing up dead in horrific numbers along our coastline. Something must change in the legislation managing our seas to stop this happening again."
Although PIB - polyisobutene, an oil additive which has a chemical mixture ranging from oils to solids - is considered to present a hazard to the marine environment, it is currently legal to discharge it in certain quantities directly into the sea.
Ms Crosby said: "Urgent action is required to prevent PIB causing further death and destruction within the marine environment through its discharge into the sea.
"In this one incident, a whole generation of seabirds of many species has been wiped out, not to mention the young they would have had this year.
"To support a campaign to change the law, we need to get a more accurate picture of just how many birds have been affected."
The Maritime and Coastguard Agency said it had been unable to trace the source of the spill, although it appears to be the same type of chemical as that which affected more than 300 birds earlier this year along a 200-mile stretch of coastline.
The Devon Wildlife Trust said the pollutant could even be from the same ship, affecting the coast once more due to a change in wind direction.
The Cornwall Wildlife Trust has today called on members of the public to record the numbers of dead birds being washed up on the coastline in an effort to understand the full extent of the pollution.
The 24-hour Marine Stranding Network Hotline can be reached on 0845 201 2626.